1. Field of the Invention
The present invention relates to am improved TAB (Tape Automated Bonding) tape offering excellent dimensional stability and superb reliability for connection with IC chips.
2. Prior Art
In recent years, TAB tape having multiple metallic conductors arranged on the surface of a base film, has been widely adopted because it enables high-density integration of circuits in a chip and improves the freedom in integration.
However, in conventional TAB tapes, the thermal expansion or contraction of a base film occurring when thermocompression bonding is performed to connect IC chips with inner leads causes a dimensional change or deteriorates connection reliability. The present invention provides designed areas of stress relief in the base film.
The present invention provides a TAB tape capable of absorbing or alleviating the thermal expansion or contraction of a base film occurring when thermocompression bonding is performed to connect inner lead tips with IC electrodes, or in particular, a TAB tape permitting the arrangement of inner leads at a very small pitch with intervals of 0.4 mm or less.
The present invention provides a TAB tape having multiple metallic conductors arranged on the surface of a base film with substantially square device holes. In the TAB tape, one or more slits are formed to provide areas of stress relief which extend outward from the corners or sides of the device holes or along the sides of the device holes.
In the present invention, an array of holes may be formed instead of or together with the foregoing slits to provide the stress relief. It is preferred that both the holes and array of slits are formed to ensure the dimensional stability and connection reliability of a TAB tape without impairing the mechanical strength of a base film.
Another embodiment of the present invention employs a base film having small holes all over the surface thereof.
According to the present invention, before metallic conductors are arranged on a base film, holes can be bored appropriately and easily. Moreover, even when the number of slits or array of holes are limited, a TAB tape according to the present invention offers excellent dimensional stability and connection reliability.
The shape of each array of holes or small holes in a base film is not limited to any specific one. However, a circle is preferred for easy etching or punching of the base film. Preferably, each of the holes has a longitudinally shape of a funnel opening into the opposite side of a surface on which metallic conductors are arranged, which contributes to further improvement in the dimensional stability of a base film.
Furthermore, a TAB tape according to the present invention may have either a so-called three-ply structure in which an adhesive layer is interposed between metallic conductors and a base film or a two-ply structure not including the adhesive layer. The two-ply structure is preferred, because slits and an array of holes can be formed easily by performing etching that involves a base film.
In a TAB tape of the present invention, multiple metallic conductors are arranged on the surface of a base film having generally square device holes, and one or more designed areas of stress relief are formed to extend outward from the corners or side of the device holes or along the sides of the device holes. When thermocompression bonding is performed to connect inner leads with IC chips, the slits or holes absorb or alleviate the thermal expansion or contraction of the base film in a direction parallel to the inner leads. This results in the improved connection reliability for connection between the inner leads and IC chip.